Lately, I have found it difficult to find time to work out. Even though I really like to exercise, commitments to work and family take up most of my time, leaving little time for a long run or a trip to the gym. The data show I’m not alone. According to the U.S. Centers for Disease Control, less than half of Americans meet the guidelines for aerobic exercise and less than a third complete the recommended amount of strengthening exercises.
My time crunch inspired me to look for a solution. When a friend told me about high-intensity interval training, or HIT, I thought it was worth checking out. HIT workouts involve short, intense bursts of activity followed by periods of active recovery. The idea is that this type of training raises your heart rate quicker and keeps it up to provide a greater benefit in a shorter period of time. But what does the evidence say?
It turns out there is a growing body of research on HIT training. One recent systematic review was published in May 2015 in the Journal of Sports Medicine. Researchers analyzed seven randomized-controlled trials with 182 participants to compare the effects of HIT with moderate-intensity exercise on vascular function. The reviewers found that HIT was more effective than traditional programs at reducing the risk of cardiovascular disease, inflammation, and insulin sensitivity. Researchers did find that the evidence was limited by the small number of participants in the studies, and called for more research on the topic.
Another systematic review published in the British Journal of Sports Medicine in 2013, which included 10 studies and 273 participants, found high-intensity training improves cardiovascular function nearly twice as much as moderate-intensity exercise in patients with lifestyle-induced chronic diseases. A third review published this year in the British Journal of Sports Medicine found that HIT improves cardiovascular fitness and body composition in youth ages 13 to 18.
And fourth review published this year investigated the safety of high-intensity training for patients with cardiovascular and metabolic diseases. The analysis measured the number of adverse health events among people with heart and metabolic disease after a single high-intensity workout. It found that about 8 percent of patients who completed a HIT workout had an adverse response — a higher number compared to previous studies on moderate-exercise. This paper find clear evidence that HIT is slightly more risky than more moderate exercise.
The take-home messages: High-intensity exercise is an efficient way to improve strength and cardiovascular health, but can be risky for people who suffer from chronic conditions such as heart disease or diabetes.
So what does a typical high-intensity workout look like? You can make almost any kind of exercise high-intensity by ramping up your speed. For example, take your favorite cardiovascular workout warm up for about 10 minutes. Then go at your maximum effort for 30 seconds. Stop and recover for 2 minutes. Repeat this up to three times, and then cool down. There are a lot of other high-intensity workouts using weights and calisthenics. I’m certainly going to look up a few options and give it a try.